Effect of trace elements on mesophilic anaerobic digestion of food wastewater and optimization of biogas production

This study aims to systematically investigate the effects of various trace elements on the anaerobic digestion process to maximize biogas production efficiency and promote the sustainable management of organic waste. The trace element injection amount was varied for each reactor (R1 to R4). In order to identify toxic substances affecting anaerobic microorganisms among the trace elements injected into the reactor, a BMP test was conducted under five different conditions (T1 to T5). Also, an Anaerobic Toxicity Assay (ATA) (E1 to E12) was conducted to determine the Maximum Non-Inhibitory Effective Concentration (MNIEC) of molybdenum (Mo), which does not inhibit anaerobic microorganisms. The experimental results showed that the digestion efficiency significantly decreased in the R1 reactor, where no trace elements were injected, with the pH dropping to 5.6 and biogas production sharply declining. In contrast, reactors R2 and R3, which received trace element injections, produced 18 L/d and 25 L/d of biogas, respectively, with R3 achieving a higher methane content of 64%. The B6 reactor, injected with a mixture of Fe, Co, Ni, and Mo, exhibited the highest digestion efficiency, producing 0.28 L/d of biogas with a methane content of 65%. Among the trace elements, iron (Fe) demonstrated the most significant impact on digestion efficiency, while molybdenum (Mo) showed a decrease in efficiency when injected in excess, leading to toxicity. The maximum non-inhibitory effective concentration of molybdenum was identified as 8.13 µg/L, with higher concentrations inhibiting the activity of anaerobic microorganisms. These findings highlight the critical role of optimizing trace element injection and assessing their toxic effects in improving the performance and stability of anaerobic digestion processes.